Standardization of a wireless local area network (WLAN) by using an 802.11 standard family significantly reduces costs of a WLAN technology. Wireless Fidelity (Wi-Fi) is a brand of a wireless network communications technology and held by the Wi-Fi Alliance, and an objective of Wi-Fi is to improve interoperability between wireless network products based on the 802.11 standards. A wireless local area network using a series of 802.11 protocols may be referred to as a Wi-Fi network.
Currently, an 802.11 standard version has been evolved from 802.11a/b to 802.11g, 802.11n, 802.11ac, and latest 802.11ax. To ensure backward compatibility and interoperability between products of different 802.11 standard versions, a mixed format (MF) preamble (preamble for short) has been defined since 802.11n. A legacy field part of the preamble is the same as a preamble field of 802.11a, both including a legacy short training field, a legacy long training field, and a legacy signal field. A preamble for a version later than 802.11n further includes, in addition to a legacy field part, a non-legacy field part that specifically includes a non-legacy signal field, a non-legacy short training field, a non-legacy long training field, and the like. The non-legacy field part of 802.11n is named as high throughput (HT, High Throughput), that is, the non-legacy field part includes: a high throughput signal field, a high throughput short training field, and a high throughput long training field. A non-legacy field part of 802.11ac is named as very high throughput (VHT), that is, the non-legacy field part includes: a very high throughput signal field A, a very high throughput short training field, and a very high throughput long training field, and a very high throughput signal field B. In the current 802.11 standard versions, distinction between protocol versions and auto-detection at a receive end may be implemented according to a modulation manner of a symbol following a preamble legacy field.
For an 802.11ax version, how to use a preamble to distinguish between protocol versions and implement rapid and reliable auto-detection of a protocol version becomes a problem to be urgently resolved.